Despite studies showing its benefits, aggressive insulin therapy has been slow to gain acceptance in clinical practice settings. One limitation is the inconvenience and poor subject acceptability of injection therapy, especially a multiple daily injection regimen. The purpose of this study is to determine in subjects with Type I diabetes mellitus whether glycemic control can be achieved at least as effectively with an intensive insulin regime involving pre-meal inhaled insulin plus twice daily subcutaneous NPH insulin as with an intensive subcutaneous insulin regimen involving pre-meal Regular insulin plus twice daily NPH given as four injections per day. The treatment regimens differ only by the route of delivery of the short acting insulin. This study will also examine the toleration and safety of inhaled insulin therapy and its effects after 6 months, if any, on measures of pulmonary function.